The present invention relates generally to wireless communications and, more particularly, to a method for uplink power allocation with subchannel allocation of multi-accessed users with constrained input, i.e., QAM signals.
In recently established standards, e.g. WiMAX, 3GPP LTE, orthogonal frequency division multiple access OFDMA has been adopted as the multiple-access solution for multiuser broadband wireless system. With OFDMA, each subchannel is exclusively assigned to only one user. With such an OFDMA solution, the interference among users is eliminated. The receiver is a simple single user receiver. One important performance measure for broadband multiuser system is the sum-capacity or sum-throughput, i.e., the total data transmission rate among all the users in the system. In that sense, the OFDMA is not a sum-throughput optimal solution.
It has been shown that OFDMA can achieve uplink sum-capacity optimum only for some channel realizations or with only a certain probability for Gaussian input. See H. Li and H. Liu, “An analysis on uplink OFDMA optimality”, in Proc. Of Vehicular Tech. Conf. (VTC)-Spring, Melbourne, Australia, May 2006. The overall throughput performance is then not sum-rate optimal. In practical systems, constrained inputs, such as quadrature amplitude modulation QAM signals are employed. Then, the OFDMA suffers more sum-throughput performance loss. IT can be shown that OFDMA cannot achieve sum-rate optimum for any channel realization with constrained input.
Accordingly, there is a need multiuser OFDM scheme to replace OFDMA to improve the throughput.